(i) Technical Field
The present invention relates to an image scanner for reading image information of a document. And the invention relates to an image scanner which is not only used alone but also used as, in particular, an image reading unit of an image forming apparatus such as a copier or a multifunction machine which utilizes image information read from a document.
(ii) Related Art
As one example of image scanners used in copiers and multifunction machines, there is one in which two carriages mounted with optical components such as an illumination lamp and reflection mirrors in a distributed manner are reciprocated under the bottom surface of a platen glass as a document stage (document placement surface) inside a case to which the platen glass is attached and an image of image information of a document placed on the platen glass is formed on an image sensor such as a CCD (charge-coupled device) linear sensor or directly formed an image carrying body such as a photoreceptor body via optical components such as an image forming lens. There is another image scanner in which even the image sensor is mounted on the carriages.
In the above image scanners, in general, the two carriages are supported so as to run on rails that are disposed along the read scanning direction which is parallel with the surface of the platen glass, and a wire drive mechanism is employed which reciprocates, at a movement distance ratio, the carriages which are connected to wires each of which is wound on and stretched between plural pulleys.
However, in this case, since the carriages are merely held by the wire on the rails, they may swing widely when vertical vibration is applied to them, as a result of which the reflection mirrors mounted thereon may be damaged, deviated in position, or subjected to other trouble. Such trouble most likely occurs when, for example, an image scanner is transported after its manufacture or in changing its installation location because unexpected impact may be exerted on it many times as external force in such a situation.
As for the carriage locations, for example, FIG. 3A shows a state that carriages 20 and 25 are located at home positions and FIG. 3B shows a state that the carriages 20 and 25 are located at transport positions.
In the image scanner of the related art, in the transport position mode, since as shown in FIG. 3B at least the one carriage 25 is located at the very end position in the read scanning direction so as to be set close to the pulleys 43, its swing width can be minimized even when vertical vibration is exerted on it. However, the following phenomenon may occur.
In the transport position mode, since the other carriage 20 merely kept in a state that it is stopped and fixed on the rails via wires 41, it may move in the read scanning direction X2 when impact is exerted on it during a transport. If this carriage is moved in the read scanning direction X2, wire portions connected to it are also moved and loosened. Those wire portions may come off the closest pulleys (e.g., the pulleys 44) on which those wire portions are wound.
One countermeasure is such that the other carriage is also fixed completely in position by pressing it against a fixedly disposed member. However, in this case, impact occurring during a transport is transmitted to the carriage via the fixedly disposed member without being weakened and may adversely affect the optical components mounted on the carriage.